$_{20}X^{40}$ and $_{21}X^{40}$ are

Substances which have identical chemical properties but differ in atomic weights are called

The element $Uuq$ (Ununquadium,atomic number $Z = 114$) contains $12.8 \%$ more neutrons compared to protons. What is the approximate mass number of it?

The mass number of an anion,$X^{3-}$,is $14$. If there are $10$ electrons in the anion,the number of neutrons in the nucleus of an atom of the element $X$ is:

What are the isotopes of chlorine? How do they differ from each other?

Isobars are atoms with